Input requirement for persistent configuration items in bcache

Input requirement for persistent configuration items in bcache

[Coly Li]

Hi folks,

Recently I start to look at the bcache on-disk superblock extension. I
still remember years ago people discussed adding some persistent
configuration itesm on disk, to avoid setting them via sysfs interface
every time after reboot.

While I am thinking about this, I do appreciate your help about the
input on which configuration item should be stored in the on-disk
superblock.

Although I am probably not able to make every required input being
persistent in the on-disk superblock, I believe your help may help me to
decide a reasonable option set.

Thank you all in advance.

Coly Li

Re: Input requirement for persistent configuration items in bcache

[Matthias Ferdinand]

On Sun, Jul 05, 2020 at 12:45:41PM +0800, Coly Li wrote:
> While I am thinking about this, I do appreciate your help about the
> input on which configuration item should be stored in the on-disk
> superblock.

Hi,

my use case is rather limited, all my bcache devices run in writeback
mode, and the only parameters I keep playing with are writeback_percent
and sequential_cutoff.

My short list of favourites:

   - cache_mode
   - writeback_percent
   - sequential_cutoff

But I vaguely remember that I used rebooting as last resort after too
much fiddling with tunables; persisting them in the superblock means
losing this reset-to-defaults method. Would be nice to have some other
way of resetting.

An alternative to modifying the superblock might be something
more out-of-band like iptables does with iptables-save and
iptables-restore: convert current settings to text, e.g. on shutdown or
at regular intervals, and restore settings on boot from this text file.

Regards
Matthias

Re: Input requirement for persistent configuration items in bcache

[Coly Li]

On 2020/7/5 17:12, Matthias Ferdinand wrote:
> On Sun, Jul 05, 2020 at 12:45:41PM +0800, Coly Li wrote:
>> While I am thinking about this, I do appreciate your help about the
>> input on which configuration item should be stored in the on-disk
>> superblock.
> 
> Hi,


Hi Matthias,

Thank you for the input.

> 
> my use case is rather limited, all my bcache devices run in writeback
> mode, and the only parameters I keep playing with are writeback_percent
> and sequential_cutoff.
> 
> My short list of favourites:
> 
>    - cache_mode
>    - writeback_percent
>    - sequential_cutoff
> 

Yes I plan to define a very limited minimum configuration set. And
rested should be configured via user space tool.

> But I vaguely remember that I used rebooting as last resort after too
> much fiddling with tunables; persisting them in the superblock means
> losing this reset-to-defaults method. Would be nice to have some other
> way of resetting.
> 
> An alternative to modifying the superblock might be something
> more out-of-band like iptables does with iptables-save and
> iptables-restore: convert current settings to text, e.g. on shutdown or
> at regular intervals, and restore settings on boot from this text file.

Yeah, I think in the same way as yours.

Coly Li

Input requirement for persistent configuration items in bcache

[Coly Li]

Hi folks,

Recently I start to look at the bcache on-disk superblock extension. I
still remember years ago people discussed adding some persistent
configuration itesm on disk, to avoid setting them via sysfs interface
every time after reboot.

While I am thinking about this, I do appreciate your help about the
input on which configuration item should be stored in the on-disk
superblock.

Although I am probably not able to make every required input being
persistent in the on-disk superblock, I believe your help may help me to
decide a reasonable option set.

Thank you all in advance.

Coly Li